Diversidad y control biológico de insectos - CyberTesis UACh ...

within-field control plots as well as surrounding untreated fields (Thacker and Dixon, 1996;
Huusela-Veistola, 1996; Duffield and Aebischer, 1994). Indeed, Jepson and Thacker (1990)
demonstrated a significant positive correlation between the scale on which the experiment
was carried out and the duration of the treatment effect. We raise concerns on spraying of
broad spectrum insecticides such as lambda-cyhalothrin to control Dalaca sp. based in our
findings because persistent negative effects were detected despite of small plot size and
absence of barriers of movement. In addition, the 4 most abundant species are spring
breeders and if egg-bearing females are removed from population, negative consequences
for that local population could extent to the next generation. The predation on items used by
adult in the current season and by the larvae in the summer and autumn could be relaxed,
increasing the chance of herbivores outbreaks. This situation would be stressed if we
consider that in practice, whole fields are treated and no control plots exist, therefore less
migrant sources are available.
While single predator taxa can, at times, have a strong impact on checking a target pest,
there is growing evidence that diverse guilds may be more effective (Koss et al., 2005).
This has been suggested for carabids (Symondson et al., 2002) as well as spiders
(Greenstone, 1999; Sunderland, 1999). Therefore, we advocated for the conservation of the
whole surface predator assemblage rather than a single species.
Conclusions.
The spring surface predator assemblage was make up mostly by carabids belonging to
Ferionomorpha nebroides (Curtis), Allendia chilensis (Dejean), Argutoridius chilensis
(Dejean) and Ferionomorpha aerea (Dejean). The spiders were represented equally by two
families, Lycosidae and Gnaphosidae, differing from spider assemblages surveyed in other
countries and agroecosystems.
No species was affected by B. bassiana at the applied dose, despite of significant numbers
of spores were present in soil (up to 15 days) and foliage (up to 7 days) and that B. bassiana
isolate B-931 was able to kill at least one carabid species in laboratory (Devotto, unpub.
data). This finding confirmed results from other field studies on mass-release of B.
bassiana, which reported than negative effects on non target species are no existent or
minimal (Lynch and Thomas, 2000). In contrast, the insecticide lambda-cyhalothrin
affected at least two carabid species and the two spider families. The recovery times of
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